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Register Transfer and Microoperations Part2

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– Manipulating the bits stored in a register Logic Microoperations 4.5 Logic Microoperations

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Clear – Logic operation can… 1)clear a group of bit values (Anding the bits to be cleared with zeros) R1(data) R2(mask) R1

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Set 2)set a group of bit values (Oring the bits to be set to ones with ones) R1(data) R2(mask) R1

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Complement Complement a group of bit values (Exclusively Or (XOR) the bits to be complemented with ones) R1(data) R2(mask) R1

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A variety of logic gates are inserted for each bit of registers. Different bitwise logical operations are selected by select signals. LOGIC CIRCUIT

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Example Extend the previous logic circuit to accommodate XNOR, NAND, NOR, and the complement of the second input. S2S1S0OutputOperation 000 X Y AND 001 X Y OR 010 X Y XOR 011AComplement A 100 (X Y) NAND 101 (X Y) NOR 110 (X Y) XNOR 111 BComplement B

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More Logic Microoperation TABLE 4-6. Sixteen Logic Microoperations X Y F 0 F 1 F 2 F 3 F 4 F 5 F 6 F 7 F 8 F 9 F 10 F 11 F 12 F 13 F 14 F TABLE 4-5. Truth Table for 16 Functions of Two Variables Boolean function Microoperation Name F 0 = 0 F 0 Clear F 1 = xy F A B AND F 2 = xy F A B F 3 = x F A Transfer A F 4 = xy F A B F 5 = y F B Transfer B F 6 = x y F A B Ex-OR F 7 = x+y F A B OR Boolean function Microoperation Name F 8 = (x+y) F A B NOR F 9 = (x y) F A B Ex-NOR F 10 = y F B Compl-B F 11 = x+y F A B F 12 = x F A Compl-A F 13 = x+y F A B F 14 = (xy) F A B NAND F 15 = 1 F all 1s set to all 1s

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Insert – The insert operation inserts a new value into a group of bits – This is done by first masking the bits and then ORing them with the required value 1) Mask 2) OR A before A before B mask B insert A after mask A B A after insert AVB

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4-6 Shift Microoperations Shift example: Shift Microoperations : Shift microoperations are used for serial transfer of data Three types of shift microoperation : Logical, Circular, and Arithmetic

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Shift Microoperations Symbolic designation Description R shl R Shift-left register R R shr R Shift-right register R R cil R Circular shift-left register R R cir R Circular shift-right register R R ashl R Arithmetic shift-left R R ashr R Arithmetic shift-right R TABLE 4-7. Shift Microoperations

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Logical Shift A logical shift transfers 0 through the serial input The bit transferred to the end position through the serial input is assumed to be 0 during a logical shift (Zero inserted) 00

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Logical Shift Example 1. Logical shift: Transfers 0 through the serial input. R1 shl R1 Logical shift-left R2 shr R2 Logical shift-right (Example) Logical shift-left

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Circular Shift The circular shift circulates the bits of the register around the two ends without loss of information

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Circular Shift Example Circular shift-left Circular shift- right (Example) Circular shift-left is shifted to

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Arithmetic Shift An arithmetic shift shifts a signed binary number to the left or right An arithmetic shift-left multiplies a signed binary number by 2 An arithmetic shift-right divides the number by 2 In arithmetic shifts the sign bit receives a special treatment

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Arithmetic Shift Right Arithmetic right-shift: Rn-1 remains unchanged; Rn-2 receives Rn-1, Rn-3 receives Rn-2, so on. For a negative number, 1 is shifted from the sign bit to the right. A negative number is represented by the 2s complement. The sign bit remained unchanged.

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Arithmetic Shift Right Arithmetic Shift Right : – Example (4) 0010 (2) – Example (-6) 1101 (-3)

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Arithmetic Shift Left LSB Carry out Sign bit R n-1 R n-2 Vs=1 : Overflow Vs=0 : use sign bit LSB 0 insert The operation is same with Logic shift-left The only difference is you need to check overflow problem

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Arithmetic Shift Left Arithmetic Shift Left : – Example (2) 0100 (4) – Example (-2) 1100 (-4)

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Arithmetic Shift Left Arithmetic Shift Left : – Example (4) 1000 (overflow) – Example (-6) 0100 (overflow)

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